Nagao Daisuke, Sakamoto Tatsuro, Konno Hiroyuki, Gu Shunchao, Konno Mikio
Department of Chemical Engineering, Graduate School of Engineering, Tohoku University, 6-6-07 Aoba, Aramaki-aza, Aoba-ku, Sendai 980-8579, Japan.
Langmuir. 2006 Dec 19;22(26):10958-62. doi: 10.1021/la061451l.
A previously proposed method of soap-free emulsion polymerization employing an amphoteric initiator, 2,2'-azobis [N-(2-carboxyethyl)-2-methylpropionamidine] tetrahydrate (VA-057), was extended to synthesize micrometer-sized polystyrene particles with low polydispersity in an acidic region of pH from 3.3 to 4.6. A buffer system of CH3COOH/CH3COONa was used for the adjustment of pH, which was aimed at effective promotion of particle coagulation in early stage of the polymerization. In these experiments, CH3COOH concentration was varied from 20 to 360 mM at a CH3COONa concentration of 10 mM. Polymer particles with an average size of 1.8 microm and low polydispersity were obtained at the CH3COOH concentration of 40 mM for the concentrations of 1.1 M styrene monomer and 10 mM initiator. To more precisely control dispersion stability of particles, experiments in which pH was stepwisely changed during the polymerization were also carried out. This polymerization method could enhance the average size of particles to 2.2 microm while retaining the monodispersity of particles. Furthermore, combination of pH stepwise change and monomer addition during the polymerization could produce particles with an average size of 3.0 microm and low polydispersity.
一种先前提出的采用两性引发剂2,2'-偶氮双[N-(2-羧乙基)-2-甲基丙脒]四水合物（VA-057）的无皂乳液聚合方法，被扩展用于在pH值为3.3至4.6的酸性区域合成低多分散性的微米级聚苯乙烯颗粒。使用CH3COOH/CH3COONa缓冲体系来调节pH值，目的是在聚合早期有效促进颗粒凝聚。在这些实验中，CH3COONa浓度为10 mM时，CH3COOH浓度在20至360 mM之间变化。对于1.1 M的苯乙烯单体浓度和10 mM的引发剂浓度，在CH3COOH浓度为40 mM时获得了平均尺寸为1.8微米且多分散性低的聚合物颗粒。为了更精确地控制颗粒的分散稳定性，还进行了在聚合过程中逐步改变pH值的实验。这种聚合方法可以在保持颗粒单分散性的同时将颗粒的平均尺寸提高到2.2微米。此外，在聚合过程中结合pH值的逐步变化和单体添加可以制备出平均尺寸为3.0微米且多分散性低的颗粒。
